This issue in a plugin:

• Bug: replacing an existing database didn't work datasette/datasette-load#9

Was caused by this code, which means connections stick around even when a database should have been replaced:

https://github.com/simonw/datasette/blob/53a3b3c80e64fa3733196b1478e4a4fc60b08fd4/datasette/database.py#L27C1-L27C32

The problem is that if you have a database with name dogs and you use remove_database() and then add_database() to try and replace it with a new database of the same name the existing threads continue to reference an old connection to that database.